error when compiling VPNC: "Incorrect register `%rdx' used with `l' suffix"
 

Hello,

I'm having a problem when compiling VPNC on Slackware64 (version 13). It's on my:
vendor_id : AuthenticAMD
cpu family : 15
model : 107
model name : AMD Athlon(tm) 64 X2 Dual Core Processor 5200+

When I start compilation, gcc finishes with such a result:
tunip.c:806: Error: Incorrect register `%rdx' used with `l' suffix

The line 806 in this file looks like that:
FD_SET(s->esp_fd, &rfds);

In fact it's not only a problem with VPNC compilation. The problem has also occured when I was compiling some different software. I don't remember what was it exactly, but I remember that it was also because of call to FD_SET().

More than fix, I'm interested in root of the problem. Can somebody explain, so that I can fix it by myself whenever the problem will reoccur? I've seen that similar problem has been already here:

http://www.linuxquestions.org/questi...%60l%27+suffix

so the knowledge is already available :)